A backlight module is often used as a light source for display devices such as Liquid Crystal Display (LCD) devices. Illumination level of the backlight can be adjusted low or high. For a high image quality, it is desirable to set the backlight level high (e.g., at the maximum) because setting the backlight level too low adversely affects the displayed image, for example by creating visual artifacts. On the other hand, as display sizes increase and devices become more portable, power conservation concerns become increasingly important. While significant power conservation would be achieved by reducing the backlight level, for example by setting the backlight level at 50% of the maximum, the images would have visual error and noticeable artifacts (e.g., in areas of bright saturated color) with a backlight level that low.
Different methods have been developed to optimize the backlight level by balancing the image quality concerns with the power conservation goals, one of which is to dynamically adjust the backlight level as image is displayed. Today, many new display panel systems utilize some form of this Dynamic Backlight Control (DBLC) to display a high-quality image while reducing power usage.
FIG. 1 depicts a peak-value method that may be used for DBLC. In utilizing DBLC, the backlight setting is adjusted periodically, for example on a frame-by-frame basis. The peak-value method checks all the pixels in a frame to determine which pixel requires the highest backlight level for proper image display, and sets the backlight level for the entire frame at the level that is required by that pixel. In other words, the peak-value method selects a backlight level that is equal to what is theoretically required for a given frame. With the peak-value method, the backlight level for a frame will not be set higher than is requested by the most demanding pixel. Hence, when there are many images that are “dark” such that the backlight level required by the most demanding pixel is low, the peak-value method offers significant power savings.
A weakness of the peak-value method is that it relies too heavily on one pixel. As a result of this reliance on a single pixel, which could be a stray pixel in a frame of hundreds of thousands of pixels, the selected backlight level is sometimes unnecessarily high. In some cases, there is a stray pixel that comes in and out of an image temporally, causing drastic frame-by-frame backlight changes that create flicker. Furthermore, the peak-value method leaves room for further power savings because in some cases, the quality of the image as a whole is uncompromised even if a small percentage of the pixels in a frame do not get the exact backlight level that is requested. Hence, a more sophisticated backlight decision making method is desired.